A. Field of the Invention
The invention relates to a damper disk assembly, and particularly a damper disk assembly for transmitting a torque and for absorbing and damping a torsional vibration.
B. Description of the Background Art
A clutch disk assembly used in a clutch mechanism in, for example, an automotive vehicle has a clutch function for releasable engagement with a flywheel, and also has damper capabilities that allow it to dampen torsional vibration. The clutch disk assembly includes a clutch coupling portion (friction surface portions), input plates fixed to the clutch coupling portion, a hub disposed radially inside the input plates, and elastic members elastically coupling the input plates to a flange of the hub in a circumferential direction. When the clutch coupling portion is biased toward the flywheel, torque is transmitted from the flywheel. Torque is transmitted to the hub via the elastic members, and then is output to a shaft extending from the transmission. When variations in torque of the engine are transmitted to the clutch disk assembly, relative rotation occurs between the input plates and the hub. As a result, the elastic members are circumferentially compressed. The clutch disk assembly further includes a friction mechanism that is arranged between the input plates and the hub for generating a frictional resistance when the relative rotation occurs therebetween. The friction mechanism includes a plurality of washers and a biasing member.
In a clutch disk assembly of a hub-separated type, the flange is separated from the hub, and is used as an intermediate member. The hub and the intermediate member are circumferentially coupled together by elastic members having a lower rigidity. In this clutch disk assembly, a maximum torsional angle between the input plates and the hub can be increased, and torsional characteristics can have first and second stages of low and high rigidities, respectively.
In a torsional vibration system defined by the clutch disk assembly, the transmission and other members, normal vibrations in rotation speed of the engine continuously cause collisions between gear teeth of connecting gears in the transmission, and thereby cause noises. For reducing the torsional vibration and associated gear noises, it is necessary to provide the elastic members with a reduced spring constant so that there is a low rigidity in the first dampening stage. However, for damping the torsional vibration such as a low frequency vibration, which causes a much larger angle of relative rotation in the clutch disk assembly, it is necessary to increase a spring constant of the elastic members functioning in the second stage of dampening. In the conventional device having such characteristics, a jumping phenomenon occurs. In other words, the operation angle jumps over the region in the first stage and enters the second stage, for example, when a torque variation is supplied during idling. The jumping phenomenon is caused by oscillations in the transmission of the inertia with respect to, the elastic members that are provided in the clutch disk assembly for the second stage of the dampening characteristics. This causes gear collision to a much higher extent than the normal gear collision due to excessive rotational variations.